Trans-p-chloro-alpha-methylcinnamic acid



2,969,389 TRANS-p-CHLORO-a-METHYLCINNAMIC ACID Donald G. Kundiger andGene F. Morris, Manhattan,

Kans., assignors to The Dow Chemical Company, Midland, Mich., acorporation of Delaware No Drawing. Filed Oct. 6, 1958, Ser. No. 765,2922 Claims. (Cl. 260-515) This invention relates totrans-pchloro-wmethylcinnamic acid having the formula 5 0120:0-0110 andchlorobenzene having the formula are reacted in the presence ofconcentrated sulfuric acid to form an intermediatetrans-p-chloro-oc-methylcinnamyl chloride and hydrogen chlorideby-product followed by hydrolysis of the trans-p-chloro-a-methylcinnamylchloride intermediate. The reaction is believed to take place throughthe following sequence of steps:

The exact amounts of the reactants are not critical and good results maybe obtained by employing substantially equimolar proportions of3,3-dichloro-2-methylacrolein, chlorobenzene and concentrated sulfuricacid. The preferred amounts are a slight molar excess of chlorobenzenewith respect to 3,3-dichloro-Z-methylacrolein and a substantial molarexcess of concentrated sulfuric' acid. Generally, a two tothree-foldmolar excess of the acid is considered preferable.

The reaction may be carried out in the temperature range of from about15 C. to 100 C. The reaction is preferably carried out by mixing thereactants at room temperature and thereafter heating the mixture. Duringthe heating, one equivalent of hydrogen chloride is" liberated andevolved fro-m the reactionmixture with the formation of the intermediateacid chloride. The hydrolysis of the intermediate acid chloride isconveniently carried out by diluting the reaction mixture with water.

This may be water, ice-water, ice or steam. When the.

water is steam, the reaction mixture steam distilled.

In a preferred method for carrying out the reaction, approximatelyequimolar proportions of 3,3-dichloro- Z-methylacrolein andchlorobenzene are mixed together and excess concentrated sulfuric acidadded thereto portionwise with stirring at ambient temperature. Theresulting mixture is then heated in the temperature range of from 70 C.to 100 C. for a period of from about 4 hours to 24 hours. Thereafter,the mixture is diluted with water to precipitate thetrans-p-chloro-a-methylcinnamic acid. The latter may be recovered andpurified by conventional methods.

is conveniently A representative operation is demonstrated by the following example.

25 grams (0.25 mole) of concentrated sulfuric acid was added withstirring over a period of one hour to a mixture of 14 grams (0.10 mole)of 3,3-dichloro-2- methylacrolein and 14 grams (0.13 mole) ofchlorobenzene. The resulting mixture was stirred for 16 hours and thenheated to C. and the stirring continued for 24 hours. During the periodof heating one equivalent of hydrogen chloride (as determined bytitration) was evolved from the reaction mixture. After completion ofheating, the nnxture was poured over cracked ice whereupon atrans-p-chloro-u-methylcinnamic acid product precipitated as a whitesolid. The latter, amounting to 3 grams, was recovered by filtration.The filtrate was steam distilled to remove the excess chlorobenzene andto obtain additional 5 grams of a transpchloro-a-methylcinnamic acidproduct as residue. The latter was dissolved in ethanol, purified withactivated charcoal and recrystallized from percent ethanol to obtain apurified product. The melting point of thetrans-p-chloro-a-methylcinnamic acid product was 168- 169 C. The producthad a carbon content of 60.67 percent, a hydrogen content of 4.54percent and a chlorine content of 18.16 percent. The theoretical valuesare 61.05 percent, 4.58 percent and 18.07 percent, re spectively. Theneutral equivalent was found to be 197. The theoretical value is 196.5.The total yield of the product amounted to 40 percent.

The structure of trans-p-chloro-a-methylcinnamic acid was established byan independent synthesis via the Perkin reaction by heating togetherp-chlorobenzaldehyde and propionic anhydride. Thetrans-p-chloro-umethylcinnamic acid obtained by this procedure melted at167-169 C. No depression of melting point was observed by mixing theproduct thus obtained with the product obtained according to the presentinvention.

As further structure proof, the product prepared according to thepresent invention was oxidized with aque- Patented Jan. 24, 1961 ouspotassium permanganate to produce p-chlorobenzoic acid melting at 245-246 C. The latter-gave no melting point depression with an authenticsample of p-chlorobenzoic acid.

Trans-p chloro-a-methylcinnamic: acid. is useful as a parasiticid'efandis adaptedto bejempl'oyed'for the control' of bacterial and fungalorganisms. In a representative operation of its use as a fungicide,complete inhibitionfof growth of the fungal organisms, Asbergillus te-reds, Penecillium digitatum and'Rhizopus higricans were obtained whenyeast agar medium containing 0.1 percent by weight of'trans-pchloro-a-methylcinnamic acid was plated, streaked with the aboveorganisms'and incubated at 30 C. for 3 days. i H

We claim:

I 1. A method for the preparation of trans-pfchloromethylcinnamic acidhavin'g the formula COOH which comprises mixing together at roomtemperature 3,3-dich1oro-2-methylacro1ein and chlorobenzene in thepresence of a concentrated sulfuric acid, and thereafter heating thereaction mixture to a temperature not in excess of 100 C. whereinhydrogen chloride is liberated and evolved therefrom to produce anintermediate transp-chloro-a-methylcinnamyl chloride, followed byhydrolysis of the latter with water.

2. A method for the preparation of trans-p-ch1oro-amethylcinnamic, acidhaving the, formula coon which comprises mixing together substantiailyequimolar proportions of 3-3-dichloro-2-methylacrolein andchlorobenzene, adding a substantial molar excess of concentratedsulfuric acid thereto, heating the resulting mixture for a period offrom about 4 hours to 20 hours at a temperature in a range of from 70 to100 C., and thereafter diluting the mixture with water.

References Cited in the file of this patent Matell Acta Chem. Scand.,vol. 9, p. 707 (1955).

1. A METHOD FOR THE PREPARATION OF TRANS-P-CHLORO-AMETHYLCINNAMIC ACIDHAVING THE FORMULA